Introduction to Diagnosis of Electrical Faults

A digital multimeter is required to quickly and accurately diagnose most electrical faults. Due to the complexity of the circuitry and the use of electronic components, a multimeter is required to safely test the electrical circuits on a Saturn vehicle. A test light should not he used to troubleshoot electrical circuits on a Saturn vehicle.

A test light is a low-resistance load on an electrical circuit. On most test lights used today, this low-resistance is 50 ohms. Since electronics are designed to be used with high-resistance circuits, using a low-resistance test light can cause damage to an electronic module. Another problem that occurs when using a test light is accuracy. During some testing procedures, you will be asked to test for a certain voltage. For example, from 8-16 volts. With a test light it is impossible to determine the difference between 7.5 volts and 8.0 volts. A digital voltmeter will display the exact voltage on a circuit.

Another problem with test lights are the sharp probe tip that is often used to probe wires. Probing a wire with a test light, or any other sharp pointed instrument, can break strands of the wires and cause future circuit failures. Also, a break in the insulation allows the wire core to act as a wick pulling in moisture, not only damaging the wire, but allowing it to enter connectors and components. This moisture can include salt, antifreeze, and other fluids as well as water. Some of these contaminants cause corrosion in the wire or connector. Corrosion increases a circuits resistance, and in electronic circuits, even a small increase in resistance can give a false reading from a sensor to an electronic module.

NOTE: Never probe secondary ignition wires, for any reason. Small pin holes in secondary ignition wires allow high voltage from the coil to arc from the wire to a metal part, external to the secondary ignition circuit. This arcing can cause the engine to miss-fire, causing a driveability complaint.